This invention relates to recording systems in magnetographic printing and more specifically to improvements in magnetic recording head arrangements, such as may employ multiplexing, which provide substantially higher speeds of recording and require fewer components.
This invention relates in particular to improvements in the recording head design described in U.S. Pat. No. 4,025,927 to Nelson and further relates to the recording system designs such as are described in U.S. Pat. No. 4,176,362 to Nelson.
In assessing the efficiency and reliability of a recording system, the combination of high recording speeds, with low power consumption (i.e. heat generated in the recording system, in particular in the minute recording zone areas of the recording elements) and minimal circuit components needed to generate and control the recording current pulses, is most important. It will be appreciated that the recording system time constant L/R (L and R are the electrical inductance and resistance respectively) is a primary parameter governing the efficiency of a recording system. Lower values of the L/R facilitate higher speeds of recording while lower R reduces the power consumption and heat generation. In the above-mentioned "362" and "927" patents, however, no particular impedance-reducing approach appears contemplated.
Moreover, while the teachings of the above-mentioned patents lend themselves to the design and fabrication of a recording system having a multiplicity of recording elements of very fine structure capable of high resolution magnetic recording, arranged in a linear array, such a recording system requires specially designed flat "blocking" diodes for the circuit arrangement providing multiplexing of the recording currents, which diodes are installed permanently between two specifically designed layers of contacts and conductors. In such a design when one or more of the diodes become defective, the replacement of the faulty diode(s) requires separation of these specially designed layers. Such a repair task becomes impractical especially when the layers are permanently epoxied or soldered together.
In a magnetic recording system having a multiplicity of recording elements without the benefit of a multiplexing scheme, every recording element would normally be controlled by at least a single switch to effect the recording of pixels. Such a system has the particularly severe drawback of requiring the direct connection of a separate and dedicated conductor, electronic switch, etc., to every recording element. This situation simply leads to the requirement for connecting numerous wires to the recording head. In a high resolution recording system with many recording elements per unit length (e.g. 250 per inch), the availability of space for the connecting sites becomes of great concern. Further, the task of actually reliably connecting and maintaining so many conductors within or in dealing with such a small dimension becomes an additional grave concern and leads to commercial impracticality.
To reduce the number of conductors and connections to the recording head, it is well known in this art to adopt a multiplexing scheme. In such a scheme the total number of connections made to the recording head is on the order of N+n, where N is the number of the groups of recording elements and n is the number of the recording elements within a group. However, multiplexing schemes require the addition of a current-blocking diode in series with each recording element, and these components must be associated with the recording head structure itself (to reduce the number of leads to the recording head), and thus are intimately related to the severely restricted dimensional requirements of the array of recording elements itself. Therefore, with the total number of diodes added to the recording system being N+n, the availability of space for installing so many components in a necessarily close distance from the recording element array, and which must nevertheless be accessible for maintenance, becomes of great concern.
In high-quality magnetographic recording, one of the most desired features of the recording system is its ability to record magnetic latent pixels on a magnetic medium uniformly such that the size of the recorded dots and the resultant forces between the toner particles and the magnetic medium are substantially uniform. It will be appreciated that this highly desired feature can be accomplished by: (1) fabricating the record head in such a way that the geometry of each of the recording elements, particularly at the recording zone, is substantially the same (i.e. of substantially equal dimensions); and (2) ensuring that the magnitude of the recording current pulses to be applied to the recording elements is substantially unvarying from element to element (i.e. in a high-quality recording system not more than .+-.10% variation in the amplitude of the recording current would be tolerable).
In a high speed recording system, variations in the circuit resistance and inductance can easily introduce intolerable variations in the amplitude of the recording currents, and thus becomes of additional concern. Because the circuit impedance and resistance of a recording system is directly related to the size, separation, length, and the type of the materials utilized in the design and construction of the conductive paths, etc., of the system, the structural design of a recording system with a multiplicity of recording elements for high quality, high speed recording is critical.
As a final consideration, the array of recording elements in particular must provide substantial uniformity from element to element, not only electrically (i.e. as to resistance and inductance), but especially geometrically at and in the vicinity of the recording zone, as otherwise uniformity of pixel size from element to element cannot be achieved. When the minute structure of the recording elements, especially at the recording zones, is fully considered it can be appreciated that very small variations in resistance or conductive path geometry will inevitably lead to non-uniformity of pixel recording. Thus, the cross-sectional dimensions of the recording elements at and in the vicinity of the recording zones, in particular, need to be geometrically and resistively uniform. At the same time the conductive path of each recording element needs to be enlarged as it extends away from the recording zone to a point where it is large enough to be conveniently connectable to the recording circuitry.
What is needed, therefore, is an improved magnetic recording system having a multiplicity of recording elements for high speed and high quality commercial utilization, with uniformity of recording from recording element to recording element and from recorded pixel to recorded pixel and the aforementioned concerns favorably resolved, and such is the principal object of this invention.
In accordance with the invention this need is solved by an integral structure within a recording system which comprises a first member defining a multiplicity of recording elements arranged substantially in parallel with one another, each recording element having a defined recording zone of minute size forming a part of a first surface of said first member, with the recording zones of said recording elements being predeterminably arranged relative to one another; and a second member having a first surface which is contiguous at least in part with said first member and including means for mounting at least a portion of the components comprising the recording circuitry, wherein the electrical resistance and inductance within said integral structure is substantially the same for each recording element.
The invention provides a compact, four-layer laminate structure mountable on a supporting substrate, in which the entire array of recording elements forms a flexible, uniquely arranged first layer, the return paths of the recording elements comprise a flexible second layer which has the dual utility of substantially reducing the recording element circuit inductance, the third layer is a rigid printed circuit board structure providing a mount for the blocking diodes and the conductive paths of the associated multiplexing scheme, and the fourth layer is a ground plane located between the first and third layers and insulated therefrom for further reducing the inductance associated to the circuitry of the first layer and for substantially minimizing the circuit inductance of the third layer.
In addition to providing substantially uniform circuit inductance and resistance from recording element to recording element, an arrangement according to the invention integrates the printed circuit board into the laminated structure, thus eliminating separate pieces which have to be connected (e.g. by soldering). As such, the process of fabricating such a structure into a one-piece assembly can now be fully automated particularly as to the etching of the individual layers, laminating the layers together, and inserting and making electrical connections to the components. The assembly fully lends itself to inexpensive, multiplexable, direct-drive arrangements (as opposed, for example, to transformer-coupled drive arrangements).